I've seen one that's a deck boat powered by one jet ski. The idea is that you power around in a boat and then float while you swim and enjoy the SeaDoo.
Problem is that it was slow as a boat and did not have the room of a good boat. Well, that and it ate a lot of fuel because the jet ski was not running at an optimum load.

Bill K,
One of my friends owned an older shuttlecraft up until this year (he might still be trying to sell it and his ski). Interesting concept, but the positioning of the jetski in the boat made the seating pretty cramped. The OP is just bizzare. I wonder how often something goes wrong with all of the different control linkages on one of those?

Bill K,
The OP is just bizzare. I wonder how often something goes wrong with all of the different control linkages on one of those?

Agreed. Docking, undocking, throttle & steering linkages, hows the thing float with no skis in it, etc. etc. One jetskier on their own is too much. 2 or more, plus all their passengers... thats a disaster.
Just a strange concept altogether. Doesn't surprise me that neither were very successful.